A helicopter swooped down on a Greek prison courtyard as its passengers fired machine guns at guards in a dramatic escape plot.

A rope was lowered down to convicted killer Panagiotis Vlastos, but the fourth attempt to break him out of jail was foiled when he was shot and the aircraft forced to land.

It was the latest in a series of bids to escape prison involving helicopters in Greece, and the first time such plans have failed.

Authorities say the chartered aircraft - carrying two armed passengers, a pilot and a technician - first tried unsuccessfully to rip off the chicken-wire fence surrounding Trikala prison with a hook dangling from a rope.

The men on board used AK47 assault rifles to fire on the prison guards as the rope was lowered, with one guard slightly injured by shards of flying glass.

He and others returned fire, injuring Vlastos, who had managed to climb into the helicopter, and the helicopter's technician.

Vlastos fell from a height of around 10 feet into the courtyard, and the helicopter was eventually grounded in the car park.

The 43-year-old is a convicted murderer and racketeer serving a life term. He had tried and failed three times before to escape from jail.

Prison officials told TV stations Mega and NET they recovered more than 500 bullets fired from the helicopter, while the Ministry of Justice said the helicopter passengers also carried - but did not use - "improvised explosive devices".

Justice Minister Antonis Roupakiotis suggested a tip-off had led to the plot being foiled, saying: "We had information that there were some jails we needed to keep an eye on, including Trikala prison."

Authorities said Vlastos was wounded in the legs but is being treated in the prison hospital because his injuries were not deemed serious enough for a transfer elsewhere.

It was not immediately clear if the pilot and flight technician had willingly participated in the escape attempt or had been forced to fly to the prison, which is 205 miles northwest of Athens.

An unnamed Albanian prisoner is also thought to have been part of the attempted escape, although it is not known whether he knew of the scheme in advance or just happened to be in the courtyard and tried to take advantage of the situation.

Vlastos was first arrested in 1994 in the murder of two members of a rival criminal gang. He was convicted last year as the behind-bars mastermind of the kidnapping of shipping tycoon Pericles Panagopoulos.

Panagopoulos was kidnapped in January 2009 and released after eight days, when a ransom of 30m euros (£26.2m) was paid.